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Don't @ me!
Faster Instance Variables with Object Shapes
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No content
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Aaron Patterson
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15 min standup
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Ruby Core Team
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Rails Core Team
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@tenderlove
mastodon.social/@tenderlove
GitHub
Cohost
Instagram
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LinkedIn: tenderlove
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No content
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Ruby Infrastructure
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Instance Variables
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Instance Variables: TMI
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Object Shapes
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YJIT
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All in 30 min! LOL
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Thanks!!
🥰🥰🥰🥰🥰🥰🥰🥰🥰
Ruby Infrastructure
YJIT team
Jemma Issroff
Maxime Chevalier-Boisvert
John Hawthorn @ GitHub
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How do IVARS work?
Don't @ me!
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Instance Variables = IVARs = IVs
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Implementing
Instance Variables
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Instance Variables
How to store them?
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
Hello.new
Instance of
Hello
IV Hash Table
IV Name IV Value
:@foo 1
:@bar 2
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Hash based implementation
If it were written in Ruby
class Object
def initialize
@ivs = {} # Magic instance variable hash
end
def instance_variable_set name, value
@ivs[name] = value
end
def instance_variable_get name
@ivs[name]
end
def instance_variable_defined? name
# ooohhh, why did he put this method in the example?
# I bet it's foreshadowing!
@ivs.key? name
end
end
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Ruby <= 1.8.X
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Tree Walking Interpreter
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
+
@foo @bar
1 2
3
Hash Lookup! Hash Lookup!
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Ruby 1.9: YARV
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YARV Execution
Code is compiled to instructions before execution
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
hi = Hello.new
hi.foo
Source Code Byte Code for "foo"
[:getivar, :@foo]
[:getivar, :@bar]
[:plus]
VM Stack
1
2
3
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Instruction Implementation
Example implementation written in Ruby
def getivar name
get_self.instance_variables[name]
end
getivar Implementation
[:getivar, :@foo]
[:getivar, :@bar]
[:plus]
Get self from
current stack frame
G
et H
ash
of IVS
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Hashes are slow
Compared to Arrays
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Hashes Use Memory
Compared to Arrays
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Lets Use an Array!
Instead of a Hash!
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Instance Variables
How to store them?
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
Hello.new
Instance of
Hello
IV Index Table
Name Index
:@foo 0
:@bar 1
Hello Class
IV Array
0 1
1 2
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Instance Variables (second instance)
How to store them?
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
Hello.new
Instance of
Hello
IV Index Table
Name Index
:@foo 0
:@bar 1
Hello Class
IV Array
0 1
1 2
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Instance Variables (many instances)
Hash table size is amortized
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
Hello.new
Instance of
Hello
IV Index Table
Name Index
:@foo 0
:@bar 1
Hello Class
IV Array
0 1
1 2
Instance of
Hello
0 1
1 2
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Instance Variables Storage Location
References are stored inside the object (it's in the computer)
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
Hello.new
Instance of
Hello
In-Memory Layout
Byte Index Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16
24
32
First IV
Second IV
Third IV
1
2
Qundef
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Storage Location Depends on Type
Objects store instance variables "in line", others in an external table
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
class PleaseDoNotDoThis < Array
def initialize
@foo = 1
@bar = 2
super
end
def foo
@foo + @bar
end
end
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Instruction Implementation
"foo" method instructions
def getivar name
# get the class
klass = get_self.class
# get the index of the ivar
index = klass.ivar_index[name]
if get_self.is_a?(Object)
# get the ivar value
get_self.instance_variables[index]
else
# do something different
end
end
getivar Implementation
[:getivar, :@foo]
[:getivar, :@bar]
[:plus]
Still doing a hash
lookup
😆
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Inline Caches
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Instruction Implementation
"foo" method instructions, with inline caches
def getivar name, cache
# If there is no cached index
unless cache.index
# get the class
klass = get_self.class
# get the index of the ivar
index = klass.ivar_index[name]
# store the index
cache.index = index
end
# get the cached index
index = cache.index
if get_self.is_a?(Object)
# get the ivar value
get_self.instance_variables[index]
else
# do something different
end
end
getivar Implementation
[:getivar, :@foo, cache]
[:getivar, :@bar, cache]
[:plus]
Find and cache
the index
Use the cached
index
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Usually No Hash Lookups!
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Cache Lookup Problem
Name to Index mapping is per class
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
class World < Hello
def initialize
@oops = "yikes!!"
super
end
end
Hello.new.foo
World.new.foo
Instance of
Hello
IV Index Table
Name Index
:@foo 0
:@bar 1
Hello Class
IV Array
0 1
1 2
Cache Index 0 and 1
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Cache Lookup Problem
Name to Index mapping is per class
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
class World < Hello
def initialize
@oops = "yikes!!"
super
end
end
Hello.new.foo
World.new.foo
IV Index Table
Name Index
:@foo 0
:@bar 1
Hello Class
Cache Index 0 and 1
Name Index
:@oops 0
:@foo 1
:@bar 2
World Class
Oops was
set
fi
rst!
Oops was
set
fi
rst!
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Use Class as a Cache Key
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Compare Class in Cache
Cache miss if no index or the class doesn't match
def getivar name, cache
# get the class
klass = get_self.class
# If there is no cached index and class doesn't match
if !(cache.index && cache.klass == klass)
# get the index of the ivar
index = klass.ivar_index[name]
# store the index
cache.index = index
# store the class
cache.klass = klass
end
# get the cached index
index = cache.index
if get_self.is_a?(Object)
# get the ivar value
get_self.instance_variables[index]
else
# do something different
end
end
Class must match
and IV index set
Return value at
index inside list
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Subclasses Cause Cache Misses
Since the class is a cache key, subclasses can't share cache with superclass
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
class World < Hello
end
hello = Hello.new
world = World.new
loop do
hello.foo
world.foo
end
IV Index Table
Name Index
:@foo 0
:@bar 1
Hello Class
Name Index
:@foo 0
:@bar 1
World Class
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🐵🔧
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class Hello
def initialize(set_bar)
@foo = 1
@bar = 2 if set_bar
@baz = 3
end
def foo
if !instance_variable_defined?(:@bar)
puts "oh!"
end
@foo + @bar.to_i
end
end
p Hello.new(true).foo # => 3
p Hello.new(false).foo # => 1
Handling "Undefined" Instance Variables
Unde
fi
ned IVs return `nil`, but how do we know it's unde
fi
ned?
IV Index Table
Name Index
:@foo 0
:@bar 1
:@baz 2
Hello Class
Hello Instance
In-Memory Layout
Byte Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16 1
24 2
32 3
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class Hello
def initialize(set_bar)
@foo = 1
@bar = 2 if set_bar
@baz = 3
end
def foo
if !instance_variable_defined?(:@bar)
puts "oh!"
end
@foo + @bar.to_i
end
end
p Hello.new(true).foo # => 3
p Hello.new(false).foo # => 1
Handling "Undefined" Instance Variables
Unde
fi
ned IVs return `nil`, but how do we know it's unde
fi
ned?
IV Index Table
Name Index
:@foo 0
:@bar 1
:@baz 2
Hello Class
Hello Instance
In-Memory Layout
Byte Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16 1
24 Qundef (0x24)
32 3
Cache Index 0 and 1
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Return `nil` for Undefined IVs
If the value stored in the array is Qundef, return nil, otherwise return the value
def getivar name, cache
# get the class
klass = get_self.class
# If there is no cached index and class doesn't match
if !(cache.index && cache.klass == klass)
# get the index of the ivar
index = klass.ivar_index[name]
# store the index
cache.index = index
# store the class
cache.klass = klass
end
# get the cached index
index = cache.index
if get_self.is_a?(Object)
# get the ivar value
iv = get_self.instance_variables[index]
if iv == Qundef
nil
else
iv
end
else
# do something different
end
end
Return nil if Qundef
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😫😫😫😫😫
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Conditionals for Reading an IV
Just a Recap!
• Is an index set?
• Do the classes match?
• Is it an "Object" type?
• Is the IV value equal to Qundef?
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JIT Compilation
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JIT Compilation
JIT compiler translates byte code to machine code
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
hi = Hello.new
hi.foo
Source Code Byte Code for "foo"
[:getivar, :@foo, cache]
[:getivar, :@bar, cache]
[:plus]
Machine Code
== BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
# getinstancevariable
# guard not immediate
0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
0x55a658d0a6e5: jne 0x55a660d0a0e5
0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
0x55a658d0a6f0: jbe 0x55a660d0a0fe
0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
0x55a658d0a704: cmp qword ptr [rax + 8], rcx
0x55a658d0a708: jne 0x55a660d0a117
0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
0x55a658d0a717: jbe 0x55a660d0a0cc
# guard embedded getivar
0x55a658d0a71d: test word ptr [rax], 0x2000
0x55a658d0a722: je 0x55a660d0a130
0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
0x55a658d0a72d: mov ecx, 8
0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
0x55a658d0a737: mov qword ptr [rbx], rcx
== BLOCK 2/5, ISEQ RANGE [3,6), 0 bytes =======================
== BLOCK 3/5, ISEQ RANGE [3,6), 69 bytes ======================
# getinstancevariable
# regenerate_branch
# getinstancevariable
# regenerate_branch
0x55a658d0a73a: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55a658d0a73e: movabs rcx, 0x7fbb2af48f20
0x55a658d0a748: cmp qword ptr [rax + 8], rcx
0x55a658d0a74c: jne 0x55a660d0a183
0x55a658d0a752: mov rax, qword ptr [r13 + 0x18]
0x55a658d0a756: cmp qword ptr [rax + 0x10], 1
0x55a658d0a75b: jbe 0x55a660d0a162
# guard embedded getivar
0x55a658d0a761: test word ptr [rax], 0x2000
0x55a658d0a766: je 0x55a660d0a19c
0x55a658d0a76c: cmp qword ptr [rax + 0x20], 0x34
0x55a658d0a771: mov ecx, 8
0x55a658d0a776: cmovne rcx, qword ptr [rax + 0x20]
0x55a658d0a77b: mov qword ptr [rbx + 8], rcx
== BLOCK 4/5, ISEQ RANGE [6,8), 0 bytes =======================
== BLOCK 5/5, ISEQ RANGE [6,9), 86 bytes ======================
# opt_plus
# regenerate_branch
# opt_plus
# guard arg0 fixnum
# regenerate_branch
0x55a658d0a77f: test byte ptr [rbx], 1
0x55a658d0a782: je 0x55a660d0a1ef
# guard arg1 fixnum
0x55a658d0a788: test byte ptr [rbx + 8], 1
0x55a658d0a78c: je 0x55a660d0a208
0x55a658d0a792: mov rax, qword ptr [rbx]
0x55a658d0a795: sub rax, 1
0x55a658d0a799: add rax, qword ptr [rbx + 8]
0x55a658d0a79d: jo 0x55a660d0a1ce
0x55a658d0a7a3: mov qword ptr [rbx], rax
# leave
# RUBY_VM_CHECK_INTS(ec)
0x55a658d0a7a6: mov eax, dword ptr [r12 + 0x24]
0x55a658d0a7ab: not eax
0x55a658d0a7ad: test dword ptr [r12 + 0x20], eax
0x55a658d0a7b2: jne 0x55a660d0a221
# pop stack frame
0x55a658d0a7b8: mov rax, r13
0x55a658d0a7bb: add rax, 0x40
0x55a658d0a7bf: mov r13, rax
Machine Code
== BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
# getinstancevariable
# guard not immediate
0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
0x55a658d0a6e5: jne 0x55a660d0a0e5
0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
0x55a658d0a6f0: jbe 0x55a660d0a0fe
0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
0x55a658d0a704: cmp qword ptr [rax + 8], rcx
0x55a658d0a708: jne 0x55a660d0a117
0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
0x55a658d0a717: jbe 0x55a660d0a0cc
# guard embedded getivar
0x55a658d0a71d: test word ptr [rax], 0x2000
0x55a658d0a722: je 0x55a660d0a130
0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
0x55a658d0a72d: mov ecx, 8
0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
0x55a658d0a737: mov qword ptr [rbx], rcx
== BLOCK 2/5, ISEQ RANGE [3,6), 0 bytes =======================
== BLOCK 3/5, ISEQ RANGE [3,6), 69 bytes ======================
# getinstancevariable
# regenerate_branch
# getinstancevariable
# regenerate_branch
0x55a658d0a73a: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55a658d0a73e: movabs rcx, 0x7fbb2af48f20
0x55a658d0a748: cmp qword ptr [rax + 8], rcx
0x55a658d0a74c: jne 0x55a660d0a183
0x55a658d0a752: mov rax, qword ptr [r13 + 0x18]
0x55a658d0a756: cmp qword ptr [rax + 0x10], 1
0x55a658d0a75b: jbe 0x55a660d0a162
# guard embedded getivar
0x55a658d0a761: test word ptr [rax], 0x2000
0x55a658d0a766: je 0x55a660d0a19c
0x55a658d0a76c: cmp qword ptr [rax + 0x20], 0x34
0x55a658d0a771: mov ecx, 8
0x55a658d0a776: cmovne rcx, qword ptr [rax + 0x20]
0x55a658d0a77b: mov qword ptr [rbx + 8], rcx
== BLOCK 4/5, ISEQ RANGE [6,8), 0 bytes =======================
== BLOCK 5/5, ISEQ RANGE [6,9), 86 bytes ======================
# opt_plus
# regenerate_branch
# opt_plus
# guard arg0 fixnum
# regenerate_branch
0x55a658d0a77f: test byte ptr [rbx], 1
0x55a658d0a782: je 0x55a660d0a1ef
# guard arg1 fixnum
0x55a658d0a788: test byte ptr [rbx + 8], 1
0x55a658d0a78c: je 0x55a660d0a208
0x55a658d0a792: mov rax, qword ptr [rbx]
0x55a658d0a795: sub rax, 1
0x55a658d0a799: add rax, qword ptr [rbx + 8]
0x55a658d0a79d: jo 0x55a660d0a1ce
0x55a658d0a7a3: mov qword ptr [rbx], rax
# leave
# RUBY_VM_CHECK_INTS(ec)
0x55a658d0a7a6: mov eax, dword ptr [r12 + 0x24]
0x55a658d0a7ab: not eax
0x55a658d0a7ad: test dword ptr [r12 + 0x20], eax
0x55a658d0a7b2: jne 0x55a660d0a221
# pop stack frame
0x55a658d0a7b8: mov rax, r13
0x55a658d0a7bb: add rax, 0x40
0x55a658d0a7bf: mov r13, rax
Machine Code
== BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
# getinstancevariable
# guard not immediate
0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
0x55a658d0a6e5: jne 0x55a660d0a0e5
0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
0x55a658d0a6f0: jbe 0x55a660d0a0fe
0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
0x55a658d0a704: cmp qword ptr [rax + 8], rcx
0x55a658d0a708: jne 0x55a660d0a117
0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
0x55a658d0a717: jbe 0x55a660d0a0cc
# guard embedded getivar
0x55a658d0a71d: test word ptr [rax], 0x2000
0x55a658d0a722: je 0x55a660d0a130
0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
0x55a658d0a72d: mov ecx, 8
0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
0x55a658d0a737: mov qword ptr [rbx], rcx
== BLOCK 2/5, ISEQ RANGE [3,6), 0 bytes =======================
== BLOCK 3/5, ISEQ RANGE [3,6), 69 bytes ======================
# getinstancevariable
# regenerate_branch
# getinstancevariable
# regenerate_branch
0x55a658d0a73a: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55a658d0a73e: movabs rcx, 0x7fbb2af48f20
0x55a658d0a748: cmp qword ptr [rax + 8], rcx
0x55a658d0a74c: jne 0x55a660d0a183
0x55a658d0a752: mov rax, qword ptr [r13 + 0x18]
0x55a658d0a756: cmp qword ptr [rax + 0x10], 1
0x55a658d0a75b: jbe 0x55a660d0a162
# guard embedded getivar
0x55a658d0a761: test word ptr [rax], 0x2000
0x55a658d0a766: je 0x55a660d0a19c
0x55a658d0a76c: cmp qword ptr [rax + 0x20], 0x34
0x55a658d0a771: mov ecx, 8
0x55a658d0a776: cmovne rcx, qword ptr [rax + 0x20]
0x55a658d0a77b: mov qword ptr [rbx + 8], rcx
== BLOCK 4/5, ISEQ RANGE [6,8), 0 bytes =======================
== BLOCK 5/5, ISEQ RANGE [6,9), 86 bytes ======================
# opt_plus
# regenerate_branch
# opt_plus
# guard arg0 fixnum
# regenerate_branch
0x55a658d0a77f: test byte ptr [rbx], 1
0x55a658d0a782: je 0x55a660d0a1ef
# guard arg1 fixnum
0x55a658d0a788: test byte ptr [rbx + 8], 1
0x55a658d0a78c: je 0x55a660d0a208
0x55a658d0a792: mov rax, qword ptr [rbx]
0x55a658d0a795: sub rax, 1
0x55a658d0a799: add rax, qword ptr [rbx + 8]
0x55a658d0a79d: jo 0x55a660d0a1ce
0x55a658d0a7a3: mov qword ptr [rbx], rax
# leave
# RUBY_VM_CHECK_INTS(ec)
0x55a658d0a7a6: mov eax, dword ptr [r12 + 0x24]
0x55a658d0a7ab: not eax
0x55a658d0a7ad: test dword ptr [r12 + 0x20], eax
0x55a658d0a7b2: jne 0x55a660d0a221
# pop stack frame
0x55a658d0a7b8: mov rax, r13
0x55a658d0a7bb: add rax, 0x40
0x55a658d0a7bf: mov r13, rax
Machine Code
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Slide 52 text
Machine Code for Reading an IV
def getivar name, cache
# get the class
klass = get_self.class
# If there is no cached index and class doesn't match
if !(cache.index && cache.klass == klass)
# get the index of the ivar
index = klass.ivar_index[name]
# store the index
cache.index = index
# store the class
cache.klass = klass
end
# get the cached index
index = cache.index
if get_self.is_a?(Object)
# get the ivar value
iv = get_self.instance_variables[index]
if iv == Qundef
nil
else
iv
end
else
# do something different
end
end
Instruction Implementation
== BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
# getinstancevariable
# guard not immediate
0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
0x55a658d0a6e5: jne 0x55a660d0a0e5
0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
0x55a658d0a6f0: jbe 0x55a660d0a0fe
0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
0x55a658d0a704: cmp qword ptr [rax + 8], rcx
0x55a658d0a708: jne 0x55a660d0a117
0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
0x55a658d0a717: jbe 0x55a660d0a0cc
# guard embedded getivar
0x55a658d0a71d: test word ptr [rax], 0x2000
0x55a658d0a722: je 0x55a660d0a130
0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
0x55a658d0a72d: mov ecx, 8
0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
0x55a658d0a737: mov qword ptr [rbx], rcx
Generated Machine Code
def getivar name, cache
# get the class
klass = get_self.class
# If there is no cached index and class doesn't match
if !(cache.index && cache.klass == klass)
# get the index of the ivar
index = klass.ivar_index[name]
# store the index
cache.index = index
# store the class
cache.klass = klass
end
# get the cached index
index = cache.index
if get_self.is_a?(Object)
# get the ivar value
iv = get_self.instance_variables[index]
if iv == Qundef
nil
else
iv
end
else
# do something different
end
end
Instruction Implementation
== BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
# getinstancevariable
# guard not immediate
0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
0x55a658d0a6e5: jne 0x55a660d0a0e5
0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
0x55a658d0a6f0: jbe 0x55a660d0a0fe
0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
0x55a658d0a704: cmp qword ptr [rax + 8], rcx
0x55a658d0a708: jne 0x55a660d0a117
0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
0x55a658d0a717: jbe 0x55a660d0a0cc
# guard embedded getivar
0x55a658d0a71d: test word ptr [rax], 0x2000
0x55a658d0a722: je 0x55a660d0a130
0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
0x55a658d0a72d: mov ecx, 8
0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
0x55a658d0a737: mov qword ptr [rbx], rcx
Generated Machine Code
def getivar name, cache
# get the class
klass = get_self.class
# If there is no cached index and class doesn't match
if !(cache.index && cache.klass == klass)
# get the index of the ivar
index = klass.ivar_index[name]
# store the index
cache.index = index
# store the class
cache.klass = klass
end
# get the cached index
index = cache.index
if get_self.is_a?(Object)
# get the ivar value
iv = get_self.instance_variables[index]
if iv == Qundef
nil
else
iv
end
else
# do something different
end
end
Instruction Implementation
== BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
# getinstancevariable
# guard not immediate
0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
0x55a658d0a6e5: jne 0x55a660d0a0e5
0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
0x55a658d0a6f0: jbe 0x55a660d0a0fe
0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
0x55a658d0a704: cmp qword ptr [rax + 8], rcx
0x55a658d0a708: jne 0x55a660d0a117
0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
0x55a658d0a717: jbe 0x55a660d0a0cc
# guard embedded getivar
0x55a658d0a71d: test word ptr [rax], 0x2000
0x55a658d0a722: je 0x55a660d0a130
0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
0x55a658d0a72d: mov ecx, 8
0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
0x55a658d0a737: mov qword ptr [rbx], rcx
Generated Machine Code
def getivar name, cache
# get the class
klass = get_self.class
# If there is no cached index and class doesn't match
if !(cache.index && cache.klass == klass)
# get the index of the ivar
index = klass.ivar_index[name]
# store the index
cache.index = index
# store the class
cache.klass = klass
end
# get the cached index
index = cache.index
if get_self.is_a?(Object)
# get the ivar value
iv = get_self.instance_variables[index]
if iv == Qundef
nil
else
iv
end
else
# do something different
end
end
Instruction Implementation
== BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
# getinstancevariable
# guard not immediate
0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
0x55a658d0a6e5: jne 0x55a660d0a0e5
0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
0x55a658d0a6f0: jbe 0x55a660d0a0fe
0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
0x55a658d0a704: cmp qword ptr [rax + 8], rcx
0x55a658d0a708: jne 0x55a660d0a117
0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
0x55a658d0a717: jbe 0x55a660d0a0cc
# guard embedded getivar
0x55a658d0a71d: test word ptr [rax], 0x2000
0x55a658d0a722: je 0x55a660d0a130
0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
0x55a658d0a72d: mov ecx, 8
0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
0x55a658d0a737: mov qword ptr [rbx], rcx
Generated Machine Code
def getivar name, cache
# get the class
klass = get_self.class
# If there is no cached index and class doesn't match
if !(cache.index && cache.klass == klass)
# get the index of the ivar
index = klass.ivar_index[name]
# store the index
cache.index = index
# store the class
cache.klass = klass
end
# get the cached index
index = cache.index
if get_self.is_a?(Object)
# get the ivar value
iv = get_self.instance_variables[index]
if iv == Qundef
nil
else
iv
end
else
# do something different
end
end
Instruction Implementation
Slide 53
Slide 53 text
93 Bytes for 1 IV
Slide 54
Slide 54 text
We Can Do Better!
Slide 55
Slide 55 text
Object Shapes
Slide 56
Slide 56 text
Not these shapes
Slide 57
Slide 57 text
No content
Slide 58
Slide 58 text
Shape Transitions on Write
Shapes form a tree representing Object properties
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
Sample Code Shape Tree
Root
id: 0
@foo
id: 1, index: 0
@bar
id: 2, index: 1
@foo
@bar
from: 0, to: 1, iv index: 0
from:1, to: 2, iv index: 1
Cache Key
Cache Key
Destination
Shape
Destination
Shape
IV Index
IV Index
Slide 59
Slide 59 text
Shape Tree
Shape Transitions on Write
Shape ID is used as the cache key
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
Sample Code
Root
id: 0
@foo
id: 1, index: 0
@bar
id: 2, index: 1
@foo
@bar
from: 0, to: 1, iv index: 0
from:1, to: 2, iv index: 1
Slide 60
Slide 60 text
Shapes Form a Graph
Slide 61
Slide 61 text
All Object Start From a
"Root Shape"
Slide 62
Slide 62 text
Objects Only Change Shape
on Writes
Slide 63
Slide 63 text
Shape ID is the Cache Key
Slide 64
Slide 64 text
Class is not a cache key
Slide 65
Slide 65 text
Object can share shapes
Hello and World can share caches
class Hello
def initialize
@foo = 1
@bar = 2
end
end
class World < Hello
def initialize
super
@baz = 3
end
end
Sample Code Shape Tree
from: 0, to: 1, iv index: 0
from:1, to: 2, iv index: 1
from:2, to: 3, iv index: 2
Root
id: 0
@foo
id: 1, index: 0
@bar
id: 2, index: 1
@baz
id:3, index:2
Shared between
Hello and World
instances
Slide 66
Slide 66 text
Cross Type Memory Amortization
Slide 67
Slide 67 text
Cross Type Cache Hits
Slide 68
Slide 68 text
Shared Shape Tree
Shape Tree is Shared
All objects use the shape tree, so more types can share info
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
class World < Hello
end
hello = Hello.new
world = World.new
loop do
hello.foo
world.foo
end
IV Index Table
Name Index
:@foo 0
:@bar 1
Hello Class
Name Index
:@foo 0
:@bar 1
World Class
Root
id: 0
@foo
id: 1, index: 0
@bar
id: 2, index: 1
Same shape on
both instances
Cache Shape 2 and 2
Slide 69
Slide 69 text
Cross Type Cache Hits
require 'harness'
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
class World < Hello
end
hello = Hello.new
world = World.new
run_benchmark(100) do
i = 0
while i < 90_000
hello.foo
world.foo
i += 1
end
end
Microbenchmark
before: ruby 3.2.0dev (2022-09-28T14:51:38Z before-shapes a05b261464) [x86_64-linux]
after: ruby 3.2.0dev (2022-11-22T05:20:45Z master 20b9d7b9fd) [x86_64-linux]
------------------- ----------- ---------- ---------- ---------- ------------ -------------
bench before (ms) stddev (%) after (ms) stddev (%) before/after after 1st itr
getivar-polymorphic 12.1 1.4 4.4 2.1 2.76 2.82
------------------- ----------- ---------- ---------- ---------- ------------ -------------
Legend:
- before/after: ratio of before/after time. Higher is better for after. Above 1 represents a speedup.
- after 1st itr: ratio of before/after time for the first benchmarking iteration.
Results
2.76x Faster
Slide 70
Slide 70 text
Memory Usage Improvements
Slide 71
Slide 71 text
Classes store their name as an IV
Slide 72
Slide 72 text
Class Name is an IV
Class names are stored as an instance variable on the class instance
class Hello
def initialize
@foo = 1
@bar = 2
end
def foo
@foo + @bar
end
end
puts Hello.name # => IV read
Slide 73
Slide 73 text
No content
Slide 74
Slide 74 text
No content
Slide 75
Slide 75 text
Not All Properties Are
Instance Variables
Slide 76
Slide 76 text
Freezing is a shape transition
Slide 77
Slide 77 text
Freezing Changes Shape
When we freeze an object, it changes shape
class Hello
def initialize
@foo = 1
@bar = 2
end
def set
@baz = 3
end
end
hello = Hello.new
hello.set
hello = Hello.new
hello.freeze
hello.set
Sample Code Shape Tree
Root
id: 0
@foo
id: 1, index: 0
@bar
id: 2, index: 1
@baz
id:3, index:2
Shape: 2
from: 0, to: 1, iv index: 0
from: 1, to: 2, iv index: 1
from: 2, to: 3, iv index: 2
Shape: 3
Shape: 2
Shape: 4
@foo
@bar
@baz
frozen
id:4
freeze
Slide 78
Slide 78 text
Set Instance Variable Instruction
Frozen check only on cache misses
def setinstancevariable iv_name, cache
if get_self.frozen?
raise "It's frozen!"
end
if cache.klass == get_self.class && cache.index
# CACHE HIT!!
# set the instance variable
else
cache.klass = get_self.class
cache.index = get_self.iv_index_table[iv_name]
# set the instance variable
end
end
Before Shapes
def setinstancevariable iv_name, cache
if cache.from_shape_id == get_self.shape_id
# CACHE HIT!!
# set the instance variable
else
if get_self.frozen?
raise "It's frozen!"
end
cache.shape_id = get_self.shape_id
# set the instance variable
end
end
After Shapes
Slide 79
Slide 79 text
Frozen Checks only on
Cache Misses
Slide 80
Slide 80 text
IV Write Performance Improvement
require 'harness'
class TheClass
def initialize
@v0 = 1
@v1 = 2
@v3 = 3
@levar = 1
end
def set_value_loop
# 1M
i = 0
while i < 1000000
# 10 times to de-emphasize loop overhead
@levar = i
@levar = i
@levar = i
@levar = i
@levar = i
@levar = i
@levar = i
@levar = i
@levar = i
@levar = i
i += 1
end
end
end
obj = TheClass.new
run_benchmark(100) do
obj.set_value_loop
end
Micro Benchmark
before: ruby 3.2.0dev (2022-09-28T14:51:38Z before-shapes a05b261464) [x86_64-linux]
after: ruby 3.2.0dev (2022-11-22T05:20:45Z master 20b9d7b9fd) [x86_64-linux]
------- ----------- ---------- ---------- ---------- ------------ -------------
bench before (ms) stddev (%) after (ms) stddev (%) before/after after 1st itr
setivar 64.0 0.7 53.0 2.5 1.21 1.19
------- ----------- ---------- ---------- ---------- ------------ -------------
Legend:
- before/after: ratio of before/after time. Higher is better for after. Above 1
represents a speedup.
- after 1st itr: ratio of before/after time for the first benchmarking iteration
Results
21% Faster
Slide 81
Slide 81 text
JIT Performance
Slide 82
Slide 82 text
Object Layout
All objects have 2 common
fi
elds: "
fl
ags" and "class"
Basic Object Layout
Byte Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16
24
32
T_OBJECT
Byte Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16 Instance Variable
24 Instance Variable
32 Instance Variable
T_ARRAY
Byte Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16 Array Element
24 Array Element
32 Array Element
Slide 83
Slide 83 text
Let's Check the Flags Field!
Slide 84
Slide 84 text
64 bits (width of a pointer)
Slide 85
Slide 85 text
Flags Bitmap Layout
Bottom 5 bits represent Object Type
Flags Bitmap
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Object Type ruby_value_type {
RUBY_T_OBJECT = 0x01, /**< @see struct ::RObject */
RUBY_T_CLASS = 0x02, /**< @see struct ::RClass and ::rb_cClass */
RUBY_T_MODULE = 0x03, /**< @see struct ::RClass and ::rb_cModule */
RUBY_T_FLOAT = 0x04, /**< @see struct ::RFloat */
RUBY_T_STRING = 0x05, /**< @see struct ::RString */
RUBY_T_REGEXP = 0x06, /**< @see struct ::RRegexp */
RUBY_T_ARRAY = 0x07, /**< @see struct ::RArray */
RUBY_T_HASH = 0x08, /**< @see struct ::RHash */
RUBY_T_STRUCT = 0x09, /**< @see struct ::RStruct */
RUBY_T_BIGNUM = 0x0a, /**< @see struct ::RBignum */
RUBY_T_FILE = 0x0b, /**< @see struct ::RFile */
RUBY_T_DATA = 0x0c, /**< @see struct ::RTypedData */
RUBY_T_MATCH = 0x0d, /**< @see struct ::RMatch */
RUBY_T_COMPLEX = 0x0e, /**< @see struct ::RComplex */
RUBY_T_RATIONAL = 0x0f, /**< @see struct ::RRational */
}
Slide 86
Slide 86 text
Flags Bitmap Layout
Bottom 12 bits have a common "meaning" (see
fl
_type.h)
Flags Bitmap
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Object Type
Object ID has
been seen?
Object.new.object_id
[].object_id
Slide 87
Slide 87 text
Flags Bitmap Layout
Bottom 12 bits have a common "meaning" (see
fl
_type.h)
Flags Bitmap
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Object Type
Object ID has
been seen?
Object.new.object_id
[].object_id
Slide 88
Slide 88 text
Flags Bitmap Layout
Object Type gives upper bits meaning
Flags Bitmap
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Object Type
Common Stu
ff
(see
fl
_type.h)
Object
Extended?
Depends on Object Type
Slide 89
Slide 89 text
T_OBJECT Extended Layout
Byte Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16 Pointer to Bu
ff
er
24
32
IV Array
Byte Value
0 Instance Variable
8 Instance Variable
16 Instance Variable
24 Instance Variable
32 Instance Variable
... ...
class Hello
def initialize
@foo = 1
@bar = 2
@baz = 3
@hoge = 4
end
end
Hello.new
T_OBJECT Layout
Byte Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16 Instance Variable
24 Instance Variable
32 Instance Variable
T_OBJECT Layout
Slide 90
Slide 90 text
Flags Bitmap Layout
Extended Bit means "read from external table"
Flags Bitmap
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Object Type
Common Stu
ff
(see
fl
_type.h)
Object
Extended?
Depends on Object Type
Slide 91
Slide 91 text
JIT Compilation
JIT compilation must write guards for assumptions
class Hello
def initialize
@foo = 1
@bar = 2
@baz = 3
@hoge = 4
end
def foo
@foo + @bar
end
end
What is the type?
Is it embedded or extended?
Is the IV Qundef?
Is the Class correct?
Slide 92
Slide 92 text
Runtime Check Locations
We need to test object type, extended bit, IV value
Flags Bitmap
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Object Type
Common Stu
ff
(see
fl
_type.h)
Object
Extended?
Depends on Object Type
Byte Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16 Instance Variable
24 Instance Variable
32 Instance Variable
Object Type
Qundef?
Right
class?
Slide 93
Slide 93 text
Machine Code for reading one IV
== BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
# getinstancevariable
# guard not immediate
0x55a658d0a6dd: test qword ptr [r13 + 0x18], 7
0x55a658d0a6e5: jne 0x55a660d0a0e5
0x55a658d0a6eb: cmp qword ptr [r13 + 0x18], 8
0x55a658d0a6f0: jbe 0x55a660d0a0fe
0x55a658d0a6f6: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55a658d0a6fa: movabs rcx, 0x7fbb2af48f20
0x55a658d0a704: cmp qword ptr [rax + 8], rcx
0x55a658d0a708: jne 0x55a660d0a117
0x55a658d0a70e: mov rax, qword ptr [r13 + 0x18]
0x55a658d0a712: cmp qword ptr [rax + 0x10], 0
0x55a658d0a717: jbe 0x55a660d0a0cc
# guard embedded getivar
0x55a658d0a71d: test word ptr [rax], 0x2000
0x55a658d0a722: je 0x55a660d0a130
0x55a658d0a728: cmp qword ptr [rax + 0x18], 0x34
0x55a658d0a72d: mov ecx, 8
0x55a658d0a732: cmovne rcx, qword ptr [rax + 0x18]
0x55a658d0a737: mov qword ptr [rbx], rcx
Generated Machine Code
Slide 94
Slide 94 text
Use Shapes to
Eliminate Checks
Slide 95
Slide 95 text
Shape ID Storage
Shape id is stored in the upper 32 bits
Flags Bitmap
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Object Type
Common Stu
ff
(see
fl
_type.h)
Depends on Object Type
Shape ID
Slide 96
Slide 96 text
Class Check Isn't Necessary
Shapes are independent of class
Flags Bitmap
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Object Type
Common Stu
ff
(see
fl
_type.h)
Object
Extended?
Depends on Object Type
Byte Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16 Instance Variable
24 Instance Variable
32 Instance Variable
Object Type
Qundef?
Right
class?
Shape ID
Slide 97
Slide 97 text
Handling "Undefined" Instance Variables
Shapes care about IV set order
class Hello
def initialize(set_bar)
@foo = 1
@bar = 2 if set_bar
@baz = 3
end
def foo
if !instance_variable_defined?(:@bar)
puts "oh!"
end
@foo + @bar.to_i
end
end
p Hello.new(true).foo # => 3
p Hello.new(false).foo # => 1
Root
id: 0
@foo
id: 1
@bar
id: 2
@baz
id: 3
@baz
id: 4
Shape 3
Shape 4
Slide 98
Slide 98 text
Handling "Undefined" Instance Variables
Shape 3 has a "bar" instance variable
class Hello
def initialize(set_bar)
@foo = 1
@bar = 2 if set_bar
@baz = 3
end
def foo
if !instance_variable_defined?(:@bar)
puts "oh!"
end
@foo + @bar.to_i
end
end
p Hello.new(true).foo # => 3
p Hello.new(false).foo # => 1
Shape 3
Root
id: 0
@foo
id: 1
@bar
id: 2
@baz
id: 3
@baz
id: 4
Slide 99
Slide 99 text
Handling "Undefined" Instance Variables
Shape 4 doesn't have a "bar" instance variable
class Hello
def initialize(set_bar)
@foo = 1
@bar = 2 if set_bar
@baz = 3
end
def foo
if !instance_variable_defined?(:@bar)
puts "oh!"
end
@foo + @bar.to_i
end
end
p Hello.new(true).foo # => 3
p Hello.new(false).foo # => 1
Shape 4
Root
id: 0
@foo
id: 1
@bar
id: 2
@baz
id: 3
@baz
id: 4
Slide 100
Slide 100 text
Class Check Isn't Necessary
Shapes are independent of class
Flags Bitmap
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Object Type
Common Stu
ff
(see
fl
_type.h)
Object
Extended?
Depends on Object Type
Byte Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16 Instance Variable
24 Instance Variable
32 Instance Variable
Object Type
Qundef?
Shape ID
Slide 101
Slide 101 text
Multiple Possible Layouts
Objects can vary in width, so there are 2 possible layouts
class Hello
def initialize
@foo = 1
@bar = 2
@baz = 3
end
def foo
@foo + @bar
end
end
Hello.new
Embedded Layout
Byte Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16 1
24 2
32 3
Extended Layout
Byte Value
0 Flags (a 64 bit bitmap)
8 Pointer to Class
16 Pointer to Bu
ff
er
24
32
IV Array
Byte Value
0 1
8 2
16 3
24 ...
32 ...
... ...
Slide 102
Slide 102 text
Multiple Possible Layouts
"Extending" adds a shape transition
class Hello
def initialize
@foo = 1
@bar = 2
@baz = 3
end
def foo
@foo + @bar
end
end
Hello.new
Extended Layout
Byte Value
0 Flags
8 Class
16
24
Byte Val
0 1
8 2
16 3
24 ...
32 ...
... ...
IV Ptr
1
2
Root
id: 0
@bar
id: 2
@foo
id: 1
EXTEND
id: 3
@baz
id: 4
Shape 4
Slide 103
Slide 103 text
Multiple Possible Layouts
"Extending" adds a shape transition
class Hello
def initialize
@foo = 1
@bar = 2
@baz = 3
end
def foo
@foo + @bar
end
end
Hello.new
Root
id: 0
@bar
id: 2
@foo
id: 1
EXTEND
id: 3
@baz
id: 4
@baz
id: 5
Embedded Layout
Byte Value
0 Flags
8 Class
16
24
32
2
3
1
Shape 5
Slide 104
Slide 104 text
Different Layouts Have Different Shapes
JIT Compiler can di
ff
erentiate based on shape id
class Hello
def initialize
@foo = 1
@bar = 2
@baz = 3
end
def foo
@foo + @bar
end
end
Hello.new
Root
id: 0
@bar
id: 2
@foo
id: 1
EXTEND
id: 3
@baz
id: 4
@baz
id: 5
Embedded Layout
Byte Value
0 Flags
8 Class
16 1
24 2
32 3
Extended Layout
Byte Value
0 Flags
8 Class
16 PTR
24
Byte Val
0 1
8 2
16 3
24 ...
32 ...
... ...
Slide 105
Slide 105 text
Extended Check Isn't Necessary
Shapes di
ff
er depending on embedded vs extended
Flags Bitmap
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Object Type
Common Stu
ff
(see
fl
_type.h)
Object
Extended?
Depends on Object Type
Object Type
Shape ID
Slide 106
Slide 106 text
Different Types, Same Shape
Di
ff
erent types can have the same shape, but IV storage is di
ff
erent
class Hello
def initialize
@foo = 1
@bar = 2
@baz = 3
end
end
Hello.new
ary = []
ary.instance_variable_set(:@foo, 4)
ary.instance_variable_set(:@bar, 5)
ary.instance_variable_set(:@baz, 6)
ary
Sample Code Shape Tree
Root
id: 0
@foo
id: 1
@bar
id: 2
@baz
id: 3
Shape 3
Shape 3
Slide 107
Slide 107 text
Different Types Store Instance
Variables Differently.
Slide 108
Slide 108 text
Assign Shape at Allocation Time
When a T_OBJECT is allocated, immediately set a new shape
class Hello
def initialize
@foo = 1
@bar = 2
@baz = 3
end
end
Hello.new
ary = []
ary.instance_variable_set(:@foo, 4)
ary.instance_variable_set(:@bar, 5)
ary.instance_variable_set(:@baz, 6)
ary
Sample Code Shape Tree
Root
id: 0
Shape 4
Shape 7
T_OBJECT
id: 1
@foo
id: 2
@bar
id: 3
@baz
id: 4
@foo
id: 5
@bar
id: 6
@baz
id: 7
Slide 109
Slide 109 text
Object Type Check Isn't Necessary
Shapes di
ff
er depending on object type
Flags Bitmap
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Object Type
Common Stu
ff
(see
fl
_type.h)
Depends on Object Type
Object Type
Shape ID
Slide 110
Slide 110 text
Only Shape ID Check is Required
Slide 111
Slide 111 text
JIT Code Comparison
Machine code for reading 1 instance variable
== BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
# getinstancevariable
# guard not immediate
0x55ce5998b6dd: test qword ptr [r13 + 0x18], 7
0x55ce5998b6e5: jne 0x55ce6198b0e5
0x55ce5998b6eb: cmp qword ptr [r13 + 0x18], 8
0x55ce5998b6f0: jbe 0x55ce6198b0fe
0x55ce5998b6f6: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55ce5998b6fa: movabs rcx, 0x7f09fd1e8f30
0x55ce5998b704: cmp qword ptr [rax + 8], rcx
0x55ce5998b708: jne 0x55ce6198b117
0x55ce5998b70e: mov rax, qword ptr [r13 + 0x18]
0x55ce5998b712: cmp qword ptr [rax + 0x10], 0
0x55ce5998b717: jbe 0x55ce6198b0cc
# guard embedded getivar
0x55ce5998b71d: test word ptr [rax], 0x2000
0x55ce5998b722: je 0x55ce6198b130
0x55ce5998b728: cmp qword ptr [rax + 0x18], 0x34
0x55ce5998b72d: mov ecx, 8
0x55ce5998b732: cmovne rcx, qword ptr [rax + 0x18]
0x55ce5998b737: mov qword ptr [rbx], rcx
Before Object Shapes
== BLOCK 1/5, ISEQ RANGE [0,3), 40 bytes ======================
# getinstancevariable
0x5594850ba13a: mov rax, qword ptr [r13 + 0x18]
# guard object is heap
0x5594850ba13e: test al, 7
0x5594850ba141: jne 0x5594850bc090
0x5594850ba147: cmp rax, 0
0x5594850ba14b: je 0x5594850bc090
# guard shape
0x5594850ba151: cmp dword ptr [rax + 4], 0x19
0x5594850ba155: jne 0x5594850bc0a9
0x5594850ba15b: mov rax, qword ptr [rax + 0x10]
0x5594850ba15f: mov qword ptr [rbx], rax
After Object Shapes
Slide 112
Slide 112 text
JIT Code Comparison
Machine code for reading 1 instance variable
== BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
# getinstancevariable
# guard not immediate
0x55ce5998b6dd: test qword ptr [r13 + 0x18], 7
0x55ce5998b6e5: jne 0x55ce6198b0e5
0x55ce5998b6eb: cmp qword ptr [r13 + 0x18], 8
0x55ce5998b6f0: jbe 0x55ce6198b0fe
0x55ce5998b6f6: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55ce5998b6fa: movabs rcx, 0x7f09fd1e8f30
0x55ce5998b704: cmp qword ptr [rax + 8], rcx
0x55ce5998b708: jne 0x55ce6198b117
0x55ce5998b70e: mov rax, qword ptr [r13 + 0x18]
0x55ce5998b712: cmp qword ptr [rax + 0x10], 0
0x55ce5998b717: jbe 0x55ce6198b0cc
# guard embedded getivar
0x55ce5998b71d: test word ptr [rax], 0x2000
0x55ce5998b722: je 0x55ce6198b130
0x55ce5998b728: cmp qword ptr [rax + 0x18], 0x34
0x55ce5998b72d: mov ecx, 8
0x55ce5998b732: cmovne rcx, qword ptr [rax + 0x18]
0x55ce5998b737: mov qword ptr [rbx], rcx
Before Object Shapes
== BLOCK 1/5, ISEQ RANGE [0,3), 40 bytes ======================
# getinstancevariable
0x5594850ba13a: mov rax, qword ptr [r13 + 0x18]
# guard object is heap
0x5594850ba13e: test al, 7
0x5594850ba141: jne 0x5594850bc090
0x5594850ba147: cmp rax, 0
0x5594850ba14b: je 0x5594850bc090
# guard shape
0x5594850ba151: cmp dword ptr [rax + 4], 0x19
0x5594850ba155: jne 0x5594850bc0a9
After Object Shapes
Make sure it's
shape 0x19
Slide 113
Slide 113 text
JIT Code Comparison
Machine code for reading 1 instance variable
== BLOCK 1/5, ISEQ RANGE [0,3), 93 bytes ======================
# getinstancevariable
# guard not immediate
0x55ce5998b6dd: test qword ptr [r13 + 0x18], 7
0x55ce5998b6e5: jne 0x55ce6198b0e5
0x55ce5998b6eb: cmp qword ptr [r13 + 0x18], 8
0x55ce5998b6f0: jbe 0x55ce6198b0fe
0x55ce5998b6f6: mov rax, qword ptr [r13 + 0x18]
# guard known class
0x55ce5998b6fa: movabs rcx, 0x7f09fd1e8f30
0x55ce5998b704: cmp qword ptr [rax + 8], rcx
0x55ce5998b708: jne 0x55ce6198b117
0x55ce5998b70e: mov rax, qword ptr [r13 + 0x18]
0x55ce5998b712: cmp qword ptr [rax + 0x10], 0
0x55ce5998b717: jbe 0x55ce6198b0cc
# guard embedded getivar
0x55ce5998b71d: test word ptr [rax], 0x2000
0x55ce5998b722: je 0x55ce6198b130
0x55ce5998b728: cmp qword ptr [rax + 0x18], 0x34
0x55ce5998b72d: mov ecx, 8
0x55ce5998b732: cmovne rcx, qword ptr [rax + 0x18]
0x55ce5998b737: mov qword ptr [rbx], rcx
Before Object Shapes
== BLOCK 1/5, ISEQ RANGE [0,3), 40 bytes ======================
# getinstancevariable
0x5594850ba13a: mov rax, qword ptr [r13 + 0x18]
# guard object is heap
0x5594850ba13e: test al, 7
0x5594850ba141: jne 0x5594850bc090
0x5594850ba147: cmp rax, 0
0x5594850ba14b: je 0x5594850bc090
# guard shape
0x5594850ba151: cmp dword ptr [rax + 4], 0x19
0x5594850ba155: jne 0x5594850bc0a9
0x5594850ba15b: mov rax, qword ptr [rax + 0x10]
0x5594850ba15f: mov qword ptr [rbx], rax
After Object Shapes
Read the IV,
and push on the
stack
Slide 114
Slide 114 text
Benchmark Comparison
Measure the cost of fetching and instance variable
class TheClass
def initialize
@v0 = 1
@v1 = 2
@v3 = 3
@levar = 1
end
def get_value_loop
sum = 0
# 1M
i = 0
while i < 1000000
# 10 times to de-emphasize loop overhead
sum += (@levar +
@levar +
@levar +
@levar +
@levar +
@levar +
@levar +
@levar +
@levar +
@levar)
i += 1
end
return sum
end
end
obj = TheClass.new
run_benchmark(100) do
obj.get_value_loop
end
Slide 115
Slide 115 text
Benchmark Results
before: ruby 3.2.0dev (2022-09-28T14:51:38Z before-shapes a05b261464) +YJIT [x86_64-linux]
after: ruby 3.2.0dev (2022-11-22T05:20:45Z master 20b9d7b9fd) +YJIT [x86_64-linux]
------- ----------- ---------- ---------- ---------- ------------ -------------
bench before (ms) stddev (%) after (ms) stddev (%) before/after after 1st itr
getivar 17.4 0.5 12.0 0.3 1.45 0.97
------- ----------- ---------- ---------- ---------- ------------ -------------
Legend:
- before/after: ratio of before/after time. Higher is better for after. Above 1 represents a speedup.
- after 1st itr: ratio of before/after time for the first benchmarking iteration.
45% Speed
up!
Slide 116
Slide 116 text
Before Shapes: 3.76x
Slide 117
Slide 117 text
After Shapes: 5.42x
Slide 118
Slide 118 text
Future: 32 byte Objects
Slide 119
Slide 119 text
TL;DR
Slide 120
Slide 120 text
Fewer Checks
Slide 121
Slide 121 text
Faster Code
Slide 122
Slide 122 text
Thank You!!